Follistatin Targets Distinct Pathways To Promote Brown Adipocyte Characteristics in Brown and White Adipose Tissues

Abstract

We previously demonstrated that Fst expression is highest in brown adipose tissue (BAT) and skeletal muscle, but is also present at substantial levels in epididymal and subcutaneous white adipose tissues (WATs). Fst promotes mouse brown preadipocyte differentiation and promotes browning during differentiation of mouse embryonic fibroblasts. Fst-transgenic (Fst-Tg) mice show substantial increases in circulating Fst levels and increased brown adipose mass. BAT of Fst-Tg mice had increased expression of brown adipose-associated markers including uncoupling protein 1 (UCP1), PRDM16, PGC-1α, and Glut4. WATs from Fst-Tg mice show upregulation of brown/beige adipose markers and significantly increased levels of phosphorylated p38 MAPK/ERK1/2 proteins compared with the wild-type (WT) mice. Pharmacological inhibition of pp38 MAPK/pERK1/2 pathway of recombinant mouse Fst (rFst) treated differentiating 3T3-L1 cells led to significant blockade of Fst-induced UCP1 protein expression. On the other hand, BAT from Fst-Tg mice or differentiating mouse BAT cells treated with rFst show dramatic increase in Myf5 protein levels as well as upregulation of Zic1 and Lhx8 gene expression. Myf5 levels were significantly downregulated in Fst knock-out embryos and small inhibitory RNA-mediated inhibition of Myf5 led to significant inhibition of UCP1, Lhx8, and Zic1 gene expression and significant blockade of Fst-induced induction of UCP1 protein expression in mouse BAT cells. Both interscapular BAT and WAT tissues from Fst-Tg mice display enhanced response to CL316,243 treatment and decreased expression of pSmad3 compared with the WT mice. Therefore, our results indicate that Fst promotes brown adipocyte characteristics in both WAT and BAT depots in vivo through distinct mechanisms.

Modulation of transforming growth factor-β/follistatin signaling and white adipose browning: therapeutic implications for obesity related disorders

“…These depot-specific differences in Epi and SC WAT are consistent with the published literature [89]. Importantly, UCP1 immunostaining was significantly higher in Fst-Tg compared to WT groups [86]. Several key markers involved in thermogenesis, fatty acid oxidation and mitochondrial biogenesis were significantly elevated in both WAT depots obtained from Fst-Tg mice compared to the WT mice [86].…”

“…Gene and protein expression analysis of Epi and SC WAT depots showed significant upregulation of Ucp1, Prdm16, Pgc-la and Glut4 expression levels [86]. Immunohistological staining of both WAT with UCP1 antibody showed more multilocular adipocytes in SC tissues compared to the Epi fat in both WT and Fst-Tg mice [86]. These depot-specific differences in Epi and SC WAT are consistent with the published literature [89].…”

“…These initial findings provided a rationale to explore the functional role of Fst in the regulation of adipose tissue metabolism in subsequent studies and identify the molecular targets responsible for Fst action on both metabolically active WAT and BAT depots. Using transgenic mice expressing Fst under myosin light chain promoter (Fst-Tg) [84], Singh et al [86] analyzed tire in vivo actions of Fst in both WAT and BAT. The group demonstrated for the first time that Fst promotes brown adipose function in beige and BAT via targeting distinct molecular pathways (Figure 2).…”

“…Increased levels of circulating Fst in the transgenic mice were associated with increased (~70%) interscapular BAT mass and upregulation of key brown adipocyte-specific markers Zic1, Lhx8 and Myf5 along with increased levels of Ucp1, Prdm16 and Glnt4 gene and protein expression. Gene and protein expression analysis of Epi and SC WAT depots showed significant upregulation of Ucp1, Prdm16, Pgc-la and Glut4 expression levels [86]. Immunohistological staining of both WAT with UCP1 antibody showed more multilocular adipocytes in SC tissues compared to the Epi fat in both WT and Fst-Tg mice [86].…”

“…Importantly, UCP1 immunostaining was significantly higher in Fst-Tg compared to WT groups [86]. Several key markers involved in thermogenesis, fatty acid oxidation and mitochondrial biogenesis were significantly elevated in both WAT depots obtained from Fst-Tg mice compared to the WT mice [86]. Notably, the expression level of key beige-specific marker Cd137 was also found to be elevated in the Fst-Tg group, suggesting that Fst is promoting browning of both Epi and SC WAT depots [86].…”